Nonlinear circuit



' 0. cs. SUITS NONLINEAR CIRCUIT March 30, '1937.

Original Filed Jan. 21, 1931 3 Sheets-Sheet 1 .ll. lrl

VOLTA G E Fig.4.

RESISTANCE 0/ F/6.3 0/? RESISTANCE 170/ #761 8.

LZHEQDU KEWKRCDU RES/STANCE I7 m Kw a m m t 0 myfim vw A mmw s March 30, 19374 5. a surrs Re. 20,317

' NONLINEAR CIRCUIT OriginalFiled Jan. 21, 1951 5 Sheets-Sheet 2 I Inventor; Chauncey G. Suits,

16 AJMZM by MI s Attorney.

'Marcbso, 1937. CGSWTS Re. 20,317

NONLINEAR CIRCUIT Original Filed Jan. 21, 1931 5 Sheets-Sheet 3 Fig. l8.

CURRENT VOLTA 6 E Ff g. l7,

INDUC TA NCE VOLTAGE Irwverwtor: H Chaunceg G. wits,

I His Attorneg.

Reissued Mar. 30, 1937 UNITED- STATES- NONLINEAR CIRCUIT Chauncey G. Suits, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York I Original No. 1,921,786, dated August 8, 1933, Serial No. 510,246, January cember 31,

21, 1931. Renewed De- 1932. Application for reissue August 3, 1935, Serial No. 34,644

14 Claim.

non-iinear relation to the impressed voltage.-

That is, as the voltage in the circuit is gradually increased the current increases substantially I linearly with the voltage until a certain value 15 of voltage is reached at which saturation of the core of the inductance takes place and the inductance of the coil resonates with the capacitance of the condenser. The current then suddenly jumps to a very high value whichis sev- 20 eral times the value of current prior to the sudden increase. As the electromotive force is increased still further, the current again increases with respect to the impressed voltage in a substantially linear relation. These circuits may be said to have the property of non-linear, or ferro,

resonance.

One of the objects of my invention is to provide means whereby the utility of circuits of the type indicated for general relay applications is greatly increased.

A further object of my invention is to providea relay circuit which does not include electron discharge devices, and which is adapted to thesensitive control of large amounts of power in response 35 to variations in a desired primary variable.

In circuits adapted to effect sensitive control of relatively large amounts-of power inthe past, either mechanical relays or a suitable type of electron discharge device have commonly been employed. I have found, however, that .by utilizing non-linear resonant circuits in combination with circuit controlling saturable reactors in the manners later to be described, the desired results may be accomplished by means entirely electrical and without employing electron discharge devices. 4

Still a further object of my invention is to provide a ferro resonant circuit having the proper degree of non-linearity to cause it to have a-maximum effect in controlling an electroresponsive de vice by means of which desired control operations are effected.

I The non-linear properties of ferro resonant circuits are particularly applicable to the problem of railway block signalling and a further object of my invention is to provide improved means utilizing this property whereby the signal circuits at one end of a block may be reliably controlled in response to the slight voltage variations which occur between the rails of the block. due to voltage impressedbetween the rails at the opposite end thereof, when a train enters the block.

The novel features which I believe to be characteristic of my invention areset forth with particularity in the appended claims. My inven-' tion itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying I drawings in which Figs.- 1, 3, 5, 6, B, 9, 10, 11, 12, 13,

14 and 15 represent different embodiments of the invention; Figs. 2, 4 and 7 represent certain characteristics of the arrangements shown in Figs. 1, 3, 6 and 8; Figs. 16, 17 and 18 represent certain of the characteristics of non-linear circuits in general, and Figs. 19 and 20 represent certain characteristics of the circuits shown in Figs. 14 and Referring to Fig. l of'the drawings, I have shown a source of alternating electromotive force I of substantially constant frequency having connected in series therewith a non-linear inductance 2, a condenser 3 and a resistance 4, these elements comprising the ferro, or non-linear, resonant circuit. This circuit possesses the nonlinear characteristic above described wherein when the impressed voltage of a circuit exceeds a certain value, the current in-the circuit suddenly jumps to a very large value and then upon further increase in voltage the current varies in a substantially linear manner with respect to the voltage. This sudden increase in current is due to the saturation of the core of the reactor 2, this core being made of any suitable magnetic material such as iron, an alloy of iron and'nickel orother suitable alloy. Connected across the condenser;- is a circuit comprising a rectifier and the direct current winding of a saturable reactor '8. she 45 alternating current winding of this reactorfis' connected in series with a source of electromotive force I and a load 8. The rectifier 5 msy se of any suitable construction, such as rectiilers of the contact type. If desired this rectifier may be of the type shown in United States Patent No.

7 1,640,335, issued August 23, 192'! to L813 0. GrOndahl. This, rectifier may likewise be'of either the full waveor half wave type. The reactor 6 is so constructed that the core thereof becomes saturated upon the sudden rise in current in the ferro resonant circuit whereupon its alternating. current winding becomes of very much reduced impedance.

The operation of the arrangement thus described is illustrated by the curve 9 in Fig. 2 in which the impressed voltage of the source I is plotted as abscissa and current flowing in the load I is plotted as ordinate. that for variations in voltage in the lower portion of the scale the impedance of the alternating current winding of the reactor 6 is very high so that the current in the circuit remains at a constant low value. At a certain fairly definite value of electromotive force of the source I the current in the load suddenly rises to a very high value indicated by the right-hand portion of the curve. Upon further increase in voltage the current in the circuit I remains constant.

I have found that by proper adjustment of the value or resistance 4 which is connected in series with the non-linear circuit when the impressed voltage I is again reduced the current suddenly falls at substantially the same impressed voltage at which the increase in current took place. This is nottrue, however, for other values of the resistance 4. Thus, for example, if the resistance I be reduced. it will be found that the increase in current takes place along the curve 9, whereas the decrease in current will take place along a curve corresponding to the curves III as shown in Fig. 2, the particular curve being dependent upon the value of the resistance l. Thus if the resistance I is of too low'a value, an operation is had analogous to the well known hysteresis efiect in that the reduction of current in the load circuit takes place at a lower impressed voltage of-the source I than does the corresponding rise in current in the load. This hysteresis eflect, however, is eliminated by increasing the resistance. If the resistance is increased beyond a value corresponding to that which gives the system the characteristic represented by the curve 9, then the hysteresis effect disappears, but the non-linear properties of the circuit are gradually lost; that is, the current in the load {will increase with respect to the voltage of source I in a manner indicated by curves I I dependent upon the value of the resistance. The value of resistance, however, may be found wherein the hysteresis eifect disappears and the non-linear properties of the circuit are preserved, as shown by the curve 8. This value of resistance is de--, pendent to a certain extent upon the resistance in parallel with the condenser, but in any particular case it can be easily determined by trial.

'It is preferable that the rectifier 5 be one in which the resistance decreases with an increase in current through the rectifier. This characteristic is obtained in rectiflers of the type comprising a copper plate having copper oxide formed thereon, together with electrodes arranged upon the copper plate and upon the oxide as shown in the above-mentioned patent to Lars O. Groudahl. This characteristic of the rectifier improves the operation of the circuit in that it tends to cause a substantially constant current in the secondary winding of the reactor i after the sudden rise in current. Thus it tends to fiatten the right-hand portion of the curve 9 shown in Fig. 2. Thus, for example, as the voltage of the source I is slowly increased there is of course a very small voltage across the rectifier 5 until the reactor 2 becomes saturated and the sudden rise in current occurs. at this point the poten- It will be seen.

tial across the condenser becomes suddenly very large. As the voltage of the source I is now still furtherincreased, the impedance of the rectifier I is diminished thereby tending to lessen the efiect of condenser 3. That is, the decrease in impedance of rectifier 5 causes the impedance of the combination comprising reactor 2 and, condenser 3 connected in parallel with the branch comprising rectifier 5 and reactor 8 to increase. 1

This eifect tends to lessen the current in the reactor 2 at a progressively decreasing rate as the voltage increases. Thus the variation in impedance of rectifier 5 tends to compensate for increase in voltage of the source I and thereby to render more constantthe degree of saturation of reactor 6 with respect to variation in voltage of the source I above the point at which the reactor 6 becomes saturated. It will be apparent that in this way not only is the right-hand portion of the characteristic 9 flattened but further a loss of power in the reactor 6 due to rise in current after the core is saturated is avoided.

With an arrangement as thus described, it will be apparent that the non-linear circuit 2-3 in combination with rectifier and reactor 6 operates as a very sensitive relay responsive to voltage of the source I to control the amount of power supplied from the source I to the load I. The relay,

however, is entirely electrical in. that it employs no mechanical moving parts, such as contact members and further it employs no electron discharge devices.

The arrangement shown in Fig. 3 is similar to that shown in, Fig. 1 with the exception that in this case the primary variable in response to which it is desired to control a supply of current irom the source I to the load 8 comprises a resistance I! connected in parallel with the condenser 3 rather than factors affecting the voltage of source I as in Fig. 1. The resistance I2 may be varied in response to anydesired primary variable such as temperature, pressure, intensity of light and the like.

The operation of this circuit is shown in Fig. 4 in which the value of the resistance I2 is plotted as abscissa and current is plotted as ordinates. If I assume that the value of the resistance I2 and the voltage of the source I, which I will assume to be constant, is such that the current flowing in the load is represented by the right-hand portion of the curve I3, i. e. such that resonance occurs. then as the resistance I2 decreases the effect of condenser 3 is diminished sufiiciently to suddenly throw the condenser 3 out of resonance with the reactor 2 thereby causing a sudden drop in current in the load 8 after which the current in the load 8 is represented by the left-hand portion of the curve I3. This operation may well be understood in view of the consideration that as the resistance I2 decreases both the real and imaginary componentsof the equivalent series im-' pedance of the combination comprising condenser 3 and resistance I2 connected in parallel increase over a very wide range in value of the resistance I2.

Fig. 5 is a modification of the circuit shown in Fig. l in which an electron discharge device is in series with the anode of the discharge device.

The impedance between the grid and cathode of .the discharge device is reduced somewhat upon increase in voltage, but the effect of the tube It in tending to diminish the current flowing in the reactor 2 will not be so great as is the case or the circuitshown in Fig. 1.

Fig. 6 shows an arrangementin which the supply of current to the load 8 is varied in response to a unidirectional electromotive force which may be represented by the potential upon resistance II. This resistance is connected in series with the direct current winding of a saturable reactor 10 II, the alternating current winding of which is connected across a source of electromotive iorce I in series with an inductance I9. The potential of the inductance I9 is supplied to the non-linear circuit 2-3 through the resistance 4. The resistance' I1 may be considered as being controlled, either with respect to the value of the resistance, or the potential thereon, in response to a primary variable, such as heat, pressure, or degree of light. This resistance thus controls the current flowing in the direct currentwinding of the reactor Il thereby varying the degree of saturation of the reactor. This, in turn, by variation of the impedance of the alternating current winding of the reactor l8 controls the potential upon inductance I9. The circuit is further modifled in that the potential of the condenser 3 is stepped up by means-of an autotransformer before rectification.

It will be apparent that the supply of alternating electromotive force to the non-linear circuit 2-3-4 may be effected without the use of inductance I9. I have found, however, that in a circuit of this kind where a reactor is employed having uni-directional magnetic'ilux an unstable condition is likely to result. That is, if we assume ,that the value of resistance II, or the potential thereon, is just at the critical value at which the reactor I8 saturates, it may occur that the reactor will alternately saturate and desatu- 40 rate in a substantially periodic way thereby causing current to be intermittently supplied to the load I. This operation results from an increase in impedance of the alternatingcurrent winding of reactor III which accompanies increase of current over a very large range in this winding. Thus, for example, as resistance I1 is gradually diminished a point will be reached at which the circuit comprising inductance 2, condenser I and alternating current winding of reactor l8 are in resonance. The current in this circuit then tends to jump suddenly to a very high value. This increase of current, however. so increases the impedance of reactor II as to destroy the resonant condition thereby causing a sudden diminution of current, this operation repeating itself in a periodic way. The period of this pulsation in any particular circuit is determined predominantly by the alternating voltage of source I and the direct current in reactor I8. Such an arrangement v is advantageous in-many applications such for flux in which the operation of the system is stable. I have found that the unstable condition can be avoided by connecting ,a linear element, such as a resistance or an inductance I9, in the manner shown. This element should be such that a substantial portion, such as of th thereon, whereas the ordinates are current in the load 8.

Fig. 8 shows a similar circuit modified in that the alternating current winding of the saturated reactor I8 is connected in shunt with the inductance I 9. Inductance I9 should be such that it carries a substantially greater current than reactor 2 and condenser 3. In this circuit the inductance I9 serves to stabilize the circuit and the inductance 20 which is connected in series with the source I serves to prevent short circuit of the source I when the reactor I8 is saturated. The characteristic of this circuit has the same formas that indicated in Fig. 4 if values of resistance I1 are considered as abscissa.

Fig. 9 shows my invention as applied to'the problem of actuating block signals in response to electromotlve force which is impressed between the track rails. Thus, for example, in this figure, 2i represents the rails of one block of a railway system, these rails being insulated from the other blocks as indicated at 22. Alternating current is supplied from the source I through a transformer 23 and reactor 2, condenser 3 being connected across the rails, these elements comprising the non-linear circuit. At the opposite end of the block-one or more saturable reactors 6, 6', B" are connected across the rails in series with the-rectifier 5. In the operation of this embodiment of the inventiona large current is normally flowing in the non-linear circuit comprising elements 2 and 3 and as a result a substantial voltage is impressed between the rails of the track causing the reactors 6, B and 6" to be saturated. The alternating-current winding of the reactor '6 may, for example, be employed to control the green lamp of the block signal system thereby indicating an unoccupied condition 01 the block. The reactors 6 and 6" may if desired be utilized to control signals in the adjacent. blocks or for any desired purpose whatever. Ifdesired of course these reactors may be omitted from the circuit. When a train comes into the block the resistance across the condenser 3 1s reduced and as a result, as Eliplained in connection with Fig. 3, the circuit 2-3 is thrown out of resonance. The voltage applied to the track is therefore greatly reduced and the reactors 6, 6' and 6" are desaturated causing a corresponding change in the various signals.

Considerable difficulties are commonly encountered in the operation of block signals in response to electromotive force between the rails due to the fact that the inherent resistance between the rails varies widely duringv diife'rent weather conditions. Thus in dry weather this resistance is high, whereas in wet weather it becomes very low. Thus in wet weather the change in voltage between the rails when a train comes into the block is very slight. The increase in resist-- ance between the rails, however, due to dry weather conditions is compensated for by variation in the resistance of the rectifier 5' to a considerable degree. Thus as the resistance between the rails increases the voltage across the: rectitier 5 tends to increasethereby causing a reduction in resistance of the rectifier which in turn reduces the resistance between the rails. In this way the resistance between the rails may be .it mbemmanmrthemr mm. m Mm mm 4% mm mwwmmmmm m mmmmmm mmmm mmmm mmmmmmm wmmmwwmmm mmwm mmmmmwmmmw w MM MW M MWMM WWW m mmmmmmmmmmmmmmmmmmmm mm mmwmmm mw wm m m mmmmmmmmm m mm mmm M mu m i mmiwm wifi .mmmrum a mm m mmmfi m mmmm ww m ma m Mm m mm mmmm mmm mm! mm mug am mmmmm m m mmmm fim mmmm Mm. wmmm mmmm m Mi M m w m m w mm a m m mmM mfimmmmfimmm mmm mmmmummy? mmmmmmmmmmwmmmmmmmmmm mmtmhvdmn. .i 1 an :2 w w a; u mm: mmmmmmmwmm mwmmmmmmm mmmmmw mmm m mmwmwmmmmwmmmw M m w. M mm q... m m M .mmfi gm... a mm mm mm? mm m m m mhwm mdmmm w M W: 3 mm m m Rum mmm mmmm MW W mam mm m mmem m mam m m mmmmmww mwmmmmh m mmw mmnw mm m a w m m m m m? m. mmmm u mmmm ammmmmfi mmimm mm m mummmfimmmmmmmmmmm mmwmmmmmmm mwawmmmnmmmmmmm mfifimmwmmmmmm nating electromotive force, a coil having a sat-w 2 becomes saturated the inductive reactance is substantially equal to the capacitive reactance tor practically all values of current. Thus it I cause the reactor 2 of Fig. 14 to saturate at a comparatively early time in each half cycle, then the current in the circuit will have the form shown in Fig. 20, this current having a substantial sine wave form during a large portion of the hall cycle when resonance occurs and having a practically zero value during the remainder of the half cycle. It will be obvious that the effective value of a wave of this 'form is substantially greater than that of a "wave shown in Fig. 18 and accordingly, when rectified, will produce a direct current ofgreat magnitude which may be used to saturate a reactance 8 of increased dimensions.

While I have shown particular embodiments of my invention, it will of course be understood that I do not wish to be limited thereto, since many modifications both in the circuit arrangement and in the instrumentalities employed may be made and I contemplate by the appended claims to cover all such modifications as fall within the true spirit and scope of my invention. What I claim as new and desire to secure by Letters Patent of the United States, is,--

1. In combination, a source of alternating electromotlve force, a circuit comprising a condenser nates with said coil only when said core is saturated, means responsive to a primary variable to control the degree of saturation of said core whereby the current in said condenser varies nonlinearly with respect to said primary variable, a winding arranged on a second saturable core, and means for controlling the saturation of said last-mentioned core in response to voltage on said condenser whereby the impedance of said winding varies between wide limits in response to relatively small changes in said' primary variable. I

2,. In combination, a circuit comprising a source of alternating electromotive force, an inductance and condenser connected across said source and arranged for non-linear resonance, a reactor having an alternating current winding and a direct current winding, said windings being arranged on a saturable core, and means to supply direct current to said direct current winding in accordance with the voltage on said condenser, said saturable core being adapted to saturate when said circuit becomes resonant.

3., In combination, a circuit comprising a source of alternating electromotiveforce, an inductance and a condenser connected in series,

means to control the current in said circuit in,

accordance witha primary variable, said inductance and condenser being so constructed that the current in said circuit varies non-linearly over a certain range of variations of said variable, a reactor having a saturable core and a direct current winding and an alternating current winding thereon, an asymmetrically conducting device connected with said direct current winding in series across said condenser, and the impedance of said asymmetrically conducting device being variable in an inverse relation with respect to the voltage on said condenser whereb;; after the core of said reactor becomes saturated further increases 01' current in said circuit are prevented.

4. In combination, a source of variable alter- .urable core and a condenser connected in series across said source, whereby the current in said coil and condenser varies nonlinearly with respect to the electromotivejforce of said 'source, and an electro-responsive device connected in parallel with said condenser, said device being so constructed that its'impedance is higher when the voltage on said condenser is low than when tromotive force of substantially constant frequency, an inductance and condenser connected in series across said source and arranged for non-linear resonance whereby the current in said circuit varies over a. wide range in response to comparatively small variations in electromotive force of said source, a circuit controlling reactor having a plurality of windings arranged on a saturable core, and a rectifier comprising a copper electrode having cuprous oxide formed thereon, one of said windings of said reactor and said rectifier being connected in series across said condenser.

7. In combination, a source of variable alternating electromotive force having substantiallyconstant frequency, a circuit comprising an inductance and condenser connected in series across said source, said inductance and condenser being arranged to produce wide variations in current' in said circuit when the voltage of said source varies within narrow limits, a circuit controlling saturable reactor, and means to control the saturation of said circuit controlling reactor in response to the voltage on said condenser whereby the impedance of said circuit controlling reactor is varied between wide limits in response to relatively small variations of said source.

8. In combination, a source of alternating electromotive force,. a non-linear resonant circuit connected across said source, means comprisinga reactor having a direct current winding for controlling the current in said non-linear resonant circuit, a source of current for energizing said winding, and means to prevent inter- .mittent pulsation of said circuit due to said' nected across said track at one-end of said block,

a saturable reactor connected to respond to electromotive force between the rails at the other end of said block, an inductance and condenser arranged for non-linear resonance in circuit between said reactor and said source of alternating electromotive force and means whereby the voltage on said condenser is rectified and supplied to said saturable reactor.

10. In combination, a block of railway track, a source of alternating electromotive force, a condenser connected across the rails at one end of the block, a saturable reactor connected in circuit between said condenser and said'source of alternating electromotive force and adapted lidcondsmenaresctcrhavingadirectcurwindim.an

vlcehavinganimpedancewhichvariuinversely wlththeimpressedvoltagetherebytocompen losate variations in impedancebetwe'en therail during diilerent weather conditions, and a sig-- nslcontrolledbyssidreactor.

ll.Inasourceoivariablealter-- nating electromotive force, a coil having a ssturable core and a condenser connectedin m'lesacroassaidsourcewherebythecurrentin respect to the electromotive force of said source.

and an electro-responsive device connected in parallel with said condenser.

. i3. In combination, an electric circuit com" prising a saturable inductance element, a capacitance element, and a resistance element arin series relation for non-linear resonance tor a critical value of voltage applied to said circuit; and an electro-responsive device connected in a parallel circuit with said capacitance 14. In combination, a source of alternating electromotive force "iird a nan-linear resonant circuit including a saturable reactor and condenser connected to be energised from said source, said non-linear circuit having a linear component of inductance such that the total inductive reactance of said non-linear circuit is substantially constant and of a value equal to the capacitive reactance 0! said condenser for substantially the whole of each halicycle oi the alternating current wave for all values of applied voltage greater than the critical voltage atwhich said non-linear circuit exhibits its initial critical rise 'in current.

CHAUNCEY G. SUITS. 

